As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIRCRAFT WAS IN A CRUISE CONFIGURATION WHEN THE PILOT NOTICED A VIBRATION FROM THE ENGINE. REDUCED POWER AND CAME BACK TO LAND AT THE DEPARTING AIRPORT WITHOUT INCIDENT. AIRCRAFT WAS BROUGHT INTO THE HANGER AND THE COWLINGS WERE REMOVED. IT WAS DISCOVERED THAT THE NR 2 CYLINDER HAD CRACKED FROM THE UPPER SPARK PLUG HOLE TO THE LOWER SPARK PLUG HOLE. NEW CYLINDER WAS ORDERED FROM MFG.